1. Field of the Invention
The present invention relates to a vibration control system for an automotive vehicle for controlling vibrations, i.e. noise, of the vehicle and, more particularly, to a vibrations control system for an automotive vehicle for controlling the vibrations of the vehicle, so adapted as to reduce the vibrations by the interference with vibrations generated from another source of vibrations.
2. Description of the Related Art
Vibration of an automotive vehicle, particularly noise of the internal combustion engine of the vehicle, i.e. first vibrations, may disturb the driver and the passengers. It is thus proposed that the first vibrations be reduced by creating vibrations for reducing the first vibrations, i.e. second vibrations, from a speaker or the like and by causing the second vibrations to interfere with the first vibrations.
For example, Japanese Patent Unexamined Publication Kokai No. 1-501,344 discloses a vibration control system of this kind, which comprises a reference signals generating unit for picking up a signal corresponding to the vibrations of a vibration source, i.e. to first vibrations, as a reference signal; a microphone for picking up the vibrations in a predetermined space of the vehicle body, in which the noise by the first vibrations causes problems; a speaker for generating second vibrations toward or inside the predetermined space thereof; an adaptive-type digital filter for creating the second vibrations to be generated from the speaker; and an algorithm operating unit for sequentially optimizing a filter coefficient of the filter. This control system can create the second vibrations by allowing the adaptive-type digital filter to adjust the gain or phase of the reference signal in accordance with the reference signal, and the filter coefficient of the adaptive-type digital filter is sequentially optimized by the algorithm operating unit so as to reduce the first vibrations detected by the microphone. Further, the least square is generally employed as the algorithm for optimization.
The vibrations control system disclosed in the above-mentioned prior patent publication has the advantage that various vibrations can be reduced, but it presents the drawbacks that the amount of computations becomes so voluminous that it is difficult to ensure a sufficient extent of responsiveness and that an arithmetic unit of high quality is required. In particular, the volume of computation becomes extremely large when the number of speakers and microphones becomes large.
From the above-mentioned point of view and in order to solve the problems inherent in the prior art control system, the present inventors have previously developed a vibrations control system for reducing the first vibrations with the fact taken into consideration that the vibrations of the engine for the automotive vehicle to be deadened, i.e. the first vibrations, are generally periodic. This vibrations control system can create the vibrations for reducing the first vibrations to an extremely great extent and it does not require an arithmetic unit of high quality.
This vibrations control system of this prior art comprises a cycle detecting means for detecting a cycle of first vibrations caused by a first vibrations source such as an engine, a second vibrations source, such as a speaker, for generating second vibrations for reducing a vibration energy of the first vibrations, a vibration detecting means, such as a microphone, for detecting the vibrations in a position of, for example, a vehicle compartment, in which the vibrations are desired to be reduced, a vibration energy setting means for setting a vibration energy of the second vibrations generated by the second vibrations source at each cycle detected by the cycle detecting means, and a correction means for correcting an output from the vibration energy setting means on the basis of an output of the vibration detecting means and a transmission characteristic between the vibration detecting means and the second vibration source.
This arrangement of the prior art vibration control system can present the advantages that it can collectively implement the processing of creating a wave form of the second vibrations and the processing of vibrations picked up by the vibration detecting means, such as the microphone, for every one cycle on the basis of the cycle detected by the cycle detecting means, thereby extremely simplifying the computation for optimizing the wave form of the second vibrations.
Further, this arrangement of the prior art vibrations control system for reducing the periodic vibrations as described hereinabove can sufficiently reduce the vibrations when the cycles of the first vibrations are constant, i.e. when the vehicle is running at a constant speed, although this prior art vibrations control system cannot compete with single-occurring vibrations or unforeseen vibrations. When the cycles of the first vibrations are varying, for example, during the time when the vehicle is being accelerated or decelerated, the prior art system suffers from the disadvantage that the vibrations cannot be reduced to a sufficient extent.
As the second vibrations for reducing the first vibrations can be set primarily by digital control, data values in the number corresponding to one cycle portion of the first vibrations are created in the form in which they exist in every sampling cycle, i.e. in the form of vector, and the data values set in each sampling cycle are created as amplitude, i.e. as a vibration energy, in each phase of the second vibrations. If the number of data becomes large, a wave form for one cycle portion becomes long resulting in a long data length. Hence, the data of the second vibrations to be generated at this time, i.e. the current data of the second vibrations, is optimized by utilizing the data of the second vibrations previously generated, i.e. the previous data of the second vibrations. If the cycle would vary, however, the numbers of the current data and the previous data, i.e. their data lengths corresponding to one cycle portion, also vary and the second vibrations cannot be optimized at its portion corresponding to the difference in the data length, resulting in a failure to reduce the first vibrations to a sufficient extent. For example, if the data length of the current data is lengthened and its data number is increased to 12 from the previous data number of 10, the number of data lacks by two for creating the data length of the current data. On the contrary, the number of data becomes in excess if the data length would be shortened.
On the other hand, even if current second vibrations would be generated in the data length of the second vibrations previously generated, the first vibrations can be reduced to a considerably great extent. Further, when the running status of the vehicle would be returned to its ordinary running status after acceleration or deceleration, the optimization proceeds and the first vibrations can be reduced to a sufficient level. However, as the first vibrations cannot be reduced sufficiently during a period of time during which the cycles of the data varies, the first vibrations cannot be said to be reduced to a satisfactory level as a whole.